Ball chair base



FIG. 1 is a perspective view of a ball chair base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is a perspective view illustrating an application of a ball chair base in environment.

The broken line showing portions of the ball chair base is for the purpose of illustrating portions of the article and forms no part of the claim. The broken line showing of a ball chair seat, wheels, and back supporter is for the purpose of illustrating environmental structure and forms no part of the claimed design. 

CLAIM The ornamental design for a ball chair base, as shown and described. 